Waveguide device with uniform output illumination

ABSTRACT

Various embodiments of waveguide devices are described. A debanding optic may be incorporated into waveguide devices, which may help supply uniform output illumination. Accordingly, various waveguide devices are able to output a substantially flat illumination profile eliminating or mitigating banding effects.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT Patent Application No.PCT/US2018/015553, entitled “Waveguide Device with Uniform OutputIllumination” to Waldern et al., filed Jan. 26, 2018, which claimspriority to U.S. Provisional Application No. 62/499,423, entitled“Waveguide Device with Uniform Output Illumination” to Waldern et al.,filed Jan. 26, 2017, and claims priority to U.S. Provisional ApplicationNo. 62/497,781, entitled “Apparatus for Homogenizing the Output from aWaveguide Device” to Waldern et al., filed Dec. 2, 2016, the disclosuresof which are incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present disclosure relates to waveguide devices and moreparticularly to waveguides having uniform output illumination.

BACKGROUND OF THE INVENTION

Waveguide optics are currently being considered for a range of displayand sensor applications for which the ability of waveguide devices tointegrate multiple optical functions into a thin, transparent,lightweight substrate is of key importance. This new approach isstimulating new product developments including near-eye displays forAugmented Reality (AR) and Virtual Reality (VR), compact Heads UpDisplay (HUDs) for aviation and road transport and sensors for biometricand laser radar (LIDAR) applications.

Waveguide devices offer many features that are attractive in HMDs andHUDs. They are thin and transparent. Wide fields of views can beobtained by recording multiple holograms and tiling the field of viewregions formed by each hologram.

BRIEF SUMMARY OF THE INVENTION

Several embodiments are directed to a waveguide device that includes atleast one optical substrate, at least one light source; at least onelight coupler, at least one light extractor, a debanding optic. The atleast one light coupler is capable of coupling incident light from thelight source with an angular bandwidth into a total internal reflection(TIR) within the at least one optical substrate such that a unique TIRangle is defined by each light incidence angle as determined at theinput grating. The at least one light extractor extracts the light fromthe optical substrate. The debanding optic is capable of mitigatingbanding effects of an illuminated pupil, such that the extracted lightis a substantially flat illumination profile having mitigated banding.

In more embodiments, the extracted light has a spatial non-uniformityless than 10%.

In further embodiments, the extracted light has a spatial non-uniformityless than 20%.

In further more embodiments, the debanding optic is an effective inputaperture such that when the optical substrate has a thickness D, theinput aperture is configured to provide a TIR angle U in the opticalsubstrate, and the angle U is calculated by 2D tan (U).

In even more embodiments, the debanding optic provides spatial variationof the light along the TIR path of at least one of diffractionefficiency, optical transmission, polarization or birefringence.

In even further embodiments, the debanding optic is at least one gratingselected from at least one input grating and at least one outputgrating. The selected at least one grating is configured to havemultiple gratings, such that each grating provides a small pupil shiftto mitigate banding.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured as a stackedswitchable grating that turns on when a voltage is applied, shiftingpupil to mitigate banding effects.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured as an array ofswitchable grating elements that can turn on a specific element when avoltage is applied, shifting pupil to mitigate banding effects

In even further more embodiments, the selected at least one grating hasa plurality of rolled K-vectors.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured to be aplurality of passive grating layers configured to shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is one or moreindex layers disposed within the optical substrate such that the one ormore index layers influences the light ray paths within the opticalsubstrate as a function of at least one of ray angle or ray position,shifting pupil to mitigate banding effects.

In even further more embodiments, at least one index layer of the one ormore index layers is a gradient index (GRIN) medium.

In even further more embodiments, the waveguide device further includesat least one reflecting surface on at least a part of an edge of theoptical substrate. The debanding optic is one or more index layersdisposed adjacent to the at least one reflecting surface such that theone or more index layers are configured to shift pupil to mitigatebanding effects.

In even further more embodiments, the debanding optic is one or moreindex layers disposed within the optical substrate such that the one ormore index layers are configured to shift pupil to mitigate bandingeffects.

In even further more embodiments, the debanding optic is an inputgrating having a leading edge able to couple the incident light suchthat a unique displacement of a ray bundle of the light relative to theleading edge of the input grating is provided by the input grating forany given incident light direction, shifting pupil to mitigate bandingeffects.

In even further more embodiments, the debanding optic is an inputgrating configured to have a variation of diffraction efficiencies suchthat a plurality of collimated incident ray paths of the incident lightis diffracted into different TIR ray paths, as determined by a ray pathinput angle, such that a projected pupil is capable of forming at aunique location within the optical substrate for each of the pluralityof collimated incident ray paths to mitigate banding effects.

In even further more embodiments, the variation of diffractionefficiencies varies along a principal waveguide direction.

In even further more embodiments, the variation of diffractionefficiencies varies in two dimensions over the aperture of the inputgrating.

In even further more embodiments, the debanding optic is a partiallyreflecting layer disposed within the optical substrate such that thepartially reflecting layer separates incident light into transmitted andreflected light, shifting pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is a polarizationmodifying layer disposed within the optical substrate such that thepolarization modifying layer separates incident light into transmittedand reflected light, shifting pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured to provide atleast two separate waveguide paths which cancel non-uniformity of lightof the extracted light for any incidence light angle, mitigating bandingeffects.

In even further more embodiments, the selected grating has crossed slantgratings used in conjunction with at least one fold grating exit pupilexpander.

In even further more embodiments, the debanding optic is an opticalcomponent within a microdisplay that provides variable effectivenumerical apertures (NA) capable of being spatially varied along atleast one direction to shift pupil shift to mitigate banding effects.

In even further more embodiments, the debanding optic is a plurality ofgrating layers within at least one grating of either at least one inputgrating or at least one output grating such that the plurality ofgrating layers is configured to smear out any fixed pattern noiseresulting in shift of pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is an inputgrating configured as an array of selectively switchable elements suchthat configuring the input grating as a switching grating array providespupil switching in vertical and horizontal directions to shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is a plurality ofrefractive index layers that provide spatial variation along each TIRpath of at least one of diffraction efficiency, optical transmission,polarization and birefringence to influence ray paths within a waveguidesubstrate as a function of at least one of ray angle or ray positionwithin the substrate, resulting in shift of pupil to mitigate bandingeffects.

In even further more embodiments, the plurality of refractive indexlayers incorporates adhesives of different indices.

In even further more embodiments, the plurality of refractive indexlayers incorporates layers selected from the group consisting ofalignment layers, isotropic refractive layers, GRIN structures,antireflection layers, partially reflecting layer, and birefringentstretched polymer layers.

In even further more embodiments, the debanding optic is a microdisplayprojecting spatially varied numerical apertures that shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is a tiltedmicrodisplay configured to project a tilted, rectangular exit pupil suchthat the cross section of the exit pupil varies with a field angle, suchthat banding effects are mitigated.

In even further more embodiments, the debanding optic is a tiltedmicrodisplay configured to angle light rays to form various projectedpupils at different positions along the optical substrate for each angleof incident light, such that banding effects are mitigated along oneexpansion axis.

In even further more embodiments, the optical substrate has a thicknessD and the debanding optic is a prism coupled to the optical substrate,such that a linear relationship between the angles of an exit pupil fromthe light source and the TIR angles in the optical substrate result inno gaps between successive light extractions along the TIR ray path,which occurs when the TIR path angle is U as defined by 2D tan (U).

In even further more embodiments, the debanding optic is alight-absorbing film adjacent to the edges of the optical substrate suchthat portions of the incident light, that would otherwise give rise tobanding, are removed, mitigating banding effects.

In even further more embodiments, the optical substrate has a thicknessD and the debanding optic is a first light-absorbing film disposedadjacent to the edges an input substrate containing an input grating anddisposed adjacent to the optical substrate, and a second light-absorbingfilm disposed adjacent to the edges a second substrate, attachedadjacent to the optical substrate opposite the input substrate, suchthat incident light results in no gaps between successive lightextractions along the TIR ray path, which occurs when the TIR path angleis U as defined by 2D tan (U).

In even further more embodiments, the thickness of the optical substrateis 3.4 mm, the thickness of the second is substrate 0.5 mm, and theinput substrate contains two 0.5 mm thick glass substrates sandwichingthe input grating.

In even further more embodiments, the debanding optic is an inputgrating configured such that the light has a unique displacementrelative to an edge of the input grating at any given incident lightdirection to shift pupil, eliminating or mitigating a banding effect.

In even further more embodiments, the device is integrated into adisplay selected from the group of head mounted display (HMD) and a headup display (HUD).

In even further more embodiments, a human eye is positioned with an exitpupil of the display.

In even further more embodiments, the device incorporates an eyetracker.

In even further more embodiments, the waveguide device further includesan input image generator that further includes the light source, amicrodisplay panel, and optics for collimating the light.

In even further more embodiments, the light source is at least onelaser.

In even further more embodiments, the light source is at least one lightemitting diode (LED).

In even further more embodiments, the light coupler is an input grating.

In even further more embodiments, the light coupler is a prism.

In even further more embodiments, the light extractor is an inputgrating.

Several embodiments are directed to a color waveguide device thatincludes at least two optical substrates, at least one light source, atleast one light coupler, at least one light extractor, and at least twoinput stops. The at least two optical substrates are stacked upon eachother. The at least one light coupler is capable of coupling incidentlight from the light source with an angular bandwidth into a totalinternal reflection (TIR) within the at least one optical substrate suchthat a unique TIR angle is defined by each light incidence angle asdetermined at the input grating. The at least one light extractorextracts the light from the optical substrate. The at least two inputstops are each within a different optical substrate, each in a differentplane, and each input stop includes an outer dichroic portion to shiftpupil and mitigate color banding.

In more embodiments, each input stop also includes an inner phasecompensation coating to compensate for a phase shift.

In further embodiments, the compensation coating includes SiO₂.

Several embodiments are directed to a method to mitigate banding in anoutput illumination of a waveguide device. The method produces incidentlight from a light source. The method passes the incident light througha light coupler to couple the incident light into an optical substratesuch that the coupled light undergoes total internal reflection (TIR)within the optical substrate. The method also extracts the TIR lightfrom the optical substrate via a light extractor to produce the outputillumination. The light passes through a debanding optic of thewaveguide device such that the debanding optic mitigates a bandingeffect of the output illumination.

In more embodiments, the output illumination has a spatialnon-uniformity less than 10%.

In further embodiments, the output illumination has a spatialnon-uniformity less than 20%.

In further more embodiments, the debanding optic is an effective inputaperture such that when the optical substrate has a thickness D, theinput aperture is configured to provide a TIR angle U in the opticalsubstrate, and the angle U is calculated by 2D tan (U).

In even more embodiments, the debanding optic provides spatial variationof the light along the TIR path of at least one of diffractionefficiency, optical transmission, polarization or birefringence.

In even further embodiments, the debanding optic is at least one gratingselected from at least one input grating and at least one outputgrating. The selected at least one grating is configured to havemultiple gratings, such that each grating provides a small pupil shiftto mitigate banding.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured as a stackedswitchable grating that turns on when a voltage is applied, shiftingpupil to mitigate banding effects.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured as an array ofswitchable grating elements that can turn on a specific element when avoltage is applied, shifting pupil to mitigate banding effects

In even further more embodiments, the selected at least one grating hasa plurality of rolled K-vectors.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating. The selected at least one grating is configured to be aplurality of passive grating layers configured to shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is one or moreindex layers disposed within the optical substrate such that the one ormore index layers influences the light ray paths within the opticalsubstrate as a function of at least one of ray angle or ray position,shifting pupil to mitigate banding effects.

In even further more embodiments, at least one index layer of the one ormore index layers is a gradient index (GRIN) medium.

In even further more embodiments, the waveguide device further includesat least one reflecting surface on at least a part of an edge of theoptical substrate. The debanding optic is one or more index layersdisposed adjacent to the at least one reflecting surface such that theone or more index layers are configured to shift pupil to mitigatebanding effects.

In even further more embodiments, the debanding optic is one or moreindex layers disposed within the optical substrate such that the one ormore index layers are configured to shift pupil to mitigate bandingeffects.

In even further more embodiments, the debanding optic is an inputgrating having a leading edge able to couple the incident light suchthat a unique displacement of a ray bundle of the light relative to theleading edge of the input grating is provided by the input grating forany given incident light direction, shifting pupil to mitigate bandingeffects.

In even further more embodiments, the debanding optic is an inputgrating configured to have a variation of diffraction efficiencies suchthat a plurality of collimated incident ray paths of the incident lightis diffracted into different TIR ray paths, as determined by a ray pathinput angle, such that a projected pupil is capable of forming at aunique location within the optical substrate for each of the pluralityof collimated incident ray paths to mitigate banding effects.

In even further more embodiments, the variation of diffractionefficiencies varies along a principal waveguide direction.

In even further more embodiments, the variation of diffractionefficiencies varies in two dimensions over the aperture of the inputgrating.

In even further more embodiments, the debanding optic is a partiallyreflecting layer disposed within the optical substrate such that thepartially reflecting layer separates incident light into transmitted andreflected light, shifting pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is a polarizationmodifying layer disposed within the optical substrate such that thepolarization modifying layer separates incident light into transmittedand reflected light, shifting pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is at least onegrating selected from at least one input grating and at least one outputgrating, and wherein the selected at least one grating is configured toprovide at least two separate waveguide paths which cancelnon-uniformity of light of the extracted light for any incidence lightangle, mitigating banding effects.

In even further more embodiments, the selected grating has crossed slantgratings used in conjunction with at least one fold grating exit pupilexpander.

In even further more embodiments, the debanding optic is an opticalcomponent within a microdisplay that provides variable effectivenumerical apertures (NA) capable of being spatially varied along atleast one direction to shift pupil shift to mitigate banding effects.

In even further more embodiments, the debanding optic is a plurality ofgrating layers within at least one grating of either at least one inputgrating or at least one output grating such that the plurality ofgrating layers is configured to smear out any fixed pattern noiseresulting in shift of pupil to mitigate banding effects.

In even further more embodiments, the debanding optic is an inputgrating configured as an array of selectively switchable elements suchthat configuring the input grating as a switching grating array providespupil switching in vertical and horizontal directions to shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is a plurality ofrefractive index layers that provide spatial variation along each TIRpath of at least one of diffraction efficiency, optical transmission,polarization and birefringence to influence ray paths within a waveguidesubstrate as a function of at least one of ray angle or ray positionwithin the substrate, resulting in shift of pupil to mitigate bandingeffects.

In even further more embodiments, the plurality of refractive indexlayers incorporates adhesives of different indices.

In even further more embodiments, the plurality of refractive indexlayers incorporate layers selected from the group consisting ofalignment layers, isotropic refractive layers, GRIN structures,antireflection layers, partially reflecting layer, and birefringentstretched polymer layers.

In even further more embodiments, the debanding optic is a microdisplayprojecting spatially varied numerical apertures that shift pupil tomitigate banding effects.

In even further more embodiments, the debanding optic is a tiltedmicrodisplay configured to project a tilted, rectangular exit pupil suchthat the cross section of the exit pupil varies with a field angle, suchthat banding effects are mitigated.

In even further more embodiments, the debanding optic is a tiltedmicrodisplay configured to angle light rays to form various projectedpupils at different positions along the optical substrate for each angleof incident light, such that banding effects are mitigated along oneexpansion axis.

In even further more embodiments, the optical substrate has a thicknessD and the debanding optic is a prism coupled to the optical substrate,such that a linear relationship between the angles of an exit pupil fromthe light source and the TIR angles in the optical substrate result inno gaps between successive light extractions along the TIR ray path,which occurs when the TIR path angle is U as defined by 2D tan (U).

In even further more embodiments, the debanding optic is alight-absorbing film adjacent to the edges of the optical substrate suchthat portions of the incident light, that would otherwise give rise tobanding, are removed, mitigating banding effects.

In even further more embodiments, the optical substrate has a thicknessD and the debanding optic is a first light-absorbing film disposedadjacent to the edges of an input substrate containing an input gratingand disposed adjacent to the optical substrate, and a secondlight-absorbing film disposed adjacent to the edges a second substrate,attached adjacent to the optical substrate opposite the input substrate,such that incident light results in no gaps between successive lightextractions along the TIR ray path, which occurs when the TIR path angleis U as defined by 2D tan (U).

In even further more embodiments, the thickness of the optical substrateis 3.4 mm, the thickness of the second is substrate 0.5 mm, and theinput substrate contains two 0.5 mm thick glass substrates sandwichingthe input grating.

In even further more embodiments, the debanding optic is an inputgrating configured such that the light has a unique displacementrelative to an edge of the input grating at any given incident lightdirection to shift pupil, eliminating or mitigating a banding effect.

In even further more embodiments, the method is performed by a displayselected from the group of head mounted display (HMD) and a head updisplay (HUD).

In even further more embodiments, a human eye is positioned with an exitpupil of the display.

In even further more embodiments, the display incorporates an eyetracker.

In even further more embodiments, the waveguide device further includesan input image generator that further comprises the light source, amicrodisplay panel, and optics for collimating the light.

In even further more embodiments, the light source is at least onelaser.

In even further more embodiments, the light source is at least one lightemitting diode (LED).

In even further more embodiments, the light coupler is an input grating.

In even further more embodiments, the light coupler is a prism.

In even further more embodiments, the light extractor is an inputgrating.

INCORPORATION BY REFERENCE

The following related issued patents and patent applications areincorporated by reference herein in their entireties: U.S. Pat. No.9,075,184 entitled COMPACT EDGE ILLUMINATED DIFFRACTIVE DISPLAY; U.S.Pat. No. 8,233,204 entitled OPTICAL DISPLAYS; PCT Application No.US2006/043938 entitled METHOD AND APPARATUS FOR PROVIDING A TRANSPARENTDISPLAY; PCT Application No. GB2012/000677 entitled WEARABLE DATADISPLAY; U.S. patent application Ser. No. 13/317,468 entitled COMPACTEDGE ILLUMINATED EYEGLASS DISPLAY; U.S. patent application Ser. No.13/869,866 entitled HOLOGRAPHIC WIDE ANGLE DISPLAY; U.S. patentapplication Ser. No. 13/844,456 entitled TRANSPARENT WAVEGUIDE DISPLAY;U.S. patent application Ser. No. 14/620,969 entitled WAVEGUIDE GRATINGDEVICE; U.S. Provisional Patent Application No. 62/176,572 entitledELECTRICALLY FOCUS TUNABLE LENS, U.S. Provisional Patent Application No.62/177,494 entitled WAVEGUIDE DEVICE INCORPORATING A LIGHT PIPE, U.S.Provisional Patent Application No. 62/071,277 entitled METHOD ANDAPPARATUS FOR GENERATING INPUT IMAGES FOR HOLOGRAPHIC WAVEGUIDEDISPLAYS; U.S. Provisional Patent Application No. 62/123,282 entitledNEAR EYE DISPLAY USING GRADIENT INDEX OPTICS; U.S. Provisional PatentApplication No. 62/124,550 entitled WAVEGUIDE DISPLAY USING GRADIENTINDEX OPTICS; U.S. Provisional Patent Application No. 62/125,064entitled OPTICAL WAVEGUIDE DISPLAYS FOR INTEGRATION Ind. WINDOWS; U.S.Provisional Patent Application No. 62/125,066 entitled OPTICAL WAVEGUIDEDISPLAYS FOR INTEGRATION Ind. WINDOWS; U.S. Provisional PatentApplication No. 62/125,089 entitled HOLOGRAPHIC WAVEGUIDE LIGHT FIELDDISPLAYS; U.S. Pat. No. 8,224,133 entitled LASER ILLUMINATION DEVICE;U.S. Pat. No. 8,565,560 entitled LASER ILLUMINATION DEVICE; U.S. Pat.No. 6,115,152 entitled HOLOGRAPHIC ILLUMINATION SYSTEM; PCT ApplicationNo. PCT/GB2013/000005 entitled CONTACT IMAGE SENSOR USING SWITCHABLEBRAGG GRATINGS; PCT Application No. PCT/GB2012/000680 entitledIMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALSAND DEVICES; PCT Application No. PCT/GB2014/000197 entitled HOLOGRAPHICWAVEGUIDE EYE TRACKER; PCT/GB2013/000210 entitled APPARATUS FOR EYETRACKING; PCT Application No. GB2013/000210 entitled APPARATUS FOR EYETRACKING; PCT/GB2015/000274 entitled HOLOGRAPHIC WAVEGUIDEOPTICALTRACKER; U.S. Pat. No. 8,903,207 entitled SYSTEM AND METHOD OFEXTENDING VERTICAL FIELD OF VIEW IN HEAD UP DISPLAY USING A WAVEGUIDECOMBINER; U.S. Pat. No. 8,639,072 entitled COMPACT WEARABLE DISPLAY;U.S. Pat. No. 8,885,112 entitled COMPACT HOLOGRAPHIC EDGE ILLUMINATEDEYEGLASS DISPLAY; U.S. Provisional Patent Application No. 62/390,271entitled HOLOGRAPHIC WAVEGUIDE DEVICES FOR USE WITH UNPOLARIZED LIGHT;U.S. Provisional Patent Application No. 62/391,333 entitled METHOD ANDAPPARATUS FOR PROVIDING A POLARIZATION SELECTIVE HOLOGRAPHIC WAVEGUIDEDEVICE; U.S. Provisional Patent Application No. 62/493,578 entitledWAVEGUIDE DISPLAY APPARATUS; U.S. Provisional Patent Application No.62/497,781 entitled APPARATUS FOR HOMOGENIZING THE OUPUT FROM AWAVEGUIDE DEVICE; PCT Application No.: PCT/GB2016000181 entitledWAVEGUIDE DISPLAY; and PCT/GB2016/00005 entitled ENVIRONMENTALLYISOLATED WAVEGUIDE DISPLAY.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to thefollowing figures, which are presented as exemplary embodiments of theinvention and should not be construed as a complete recitation of thescope of the invention, wherein:

FIG. 1A provides a schematic cross section view of a waveguideexhibiting banding in one embodiment.

FIG. 1B provides a chart showing the integration of light extracted froma waveguide to provide debanded illumination in one embodiment.

FIG. 2 provides a schematic plan view of a detail of a waveguideillustrating a geometrical optical condition for debanding to occur inone embodiment.

FIG. 3 provides a chart showing the spatial variation of an opticalcharacteristic of an optical layer used to provide a pupil shiftingmeans in one embodiment.

FIG. 4 provides a schematic cross section view of a waveguide using aswitchable input grating in one embodiment.

FIG. 5 provides a schematic cross section view of a waveguide using aswitchable output grating in one embodiment.

FIG. 6A provides a schematic cross section view of a waveguide using aswitchable input grating array in one embodiment.

FIG. 6B provides a detail of a switchable grating showing rolledK-vectors in one embodiment.

FIG. 7 provides a schematic plan view of a switchable input gratingarray in one embodiment.

FIG. 8 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is an optical beam modifying layerdisposed on a reflecting surface of the waveguide substrate.

FIG. 9 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is an optical beam modifying layerdisposed within the waveguide substrate.

FIG. 10 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is an input grating, varying theseparation of an input beam from a leading edge of the input grating asa function of the beam incidence angle in one embodiment.

FIG. 11 provides a schematic cross section view of a detail of awaveguide in which a debanding optic provides projected pupils withinthe waveguide at locations dependent on the beam incidence angle in oneembodiment.

FIG. 12 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a partially reflecting layer inone embodiment.

FIG. 13 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a polarization rotation layer inone embodiment.

FIG. 14 provides a schematic plan view of a waveguide in which adebanding optic is a grating that provides separated light paths throughthe waveguide for different polarizations of the input light in oneembodiment.

FIG. 15 provides a schematic cross section view of a detail of amicrodisplay in which a debanding optic provides a variable numericalaperture across principal directions of a microdisplay panel in oneembodiment.

FIG. 16A provides a schematic cross section view of a waveguide usingstacked switching input gratings in one embodiment.

FIG. 16B provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a switchable input grating arrayin one embodiment.

FIG. 16C provides a schematic cross section view of a detail of awaveguide in which a debanding optic is an optical beam modifying layerdisposed within the waveguide substrate in one embodiment.

FIG. 16D provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a microdisplay panel thatprovides a variable numerical aperture across principal directions of inone embodiment.

FIG. 16E provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a tilted input image generatorproviding an exit pupil in one embodiment.

FIG. 16F provides a schematic cross section view of a detail of awaveguide in which a debanding optic a tilted input image generatorproviding an exit pupil and various projected pupils in one embodiment.

FIG. 16G provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a tilted input image generatorand a coupling prism in one embodiment.

FIG. 16H provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a plurality of additionalsubstrates having light absorbing edges in one embodiment.

FIG. 17 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a plurality of additionalsubstrates having light absorbing edges in one embodiment.

FIG. 18 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is a tilted input image generatorand a coupling prism in one embodiment.

FIG. 19 provides a schematic cross section of a coating structure foruse in balancing color registration in color display in one embodiment.

FIG. 20 provides a schematic cross section view of a detail of awaveguide in which a debanding optic is an input grating offsetting theinput beam cross section from its edge.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, systems and methods relating to near-eyedisplay or head up display systems are shown according to variousembodiments. A number of embodiments are directed to waveguide devicesfor use in near-eye display or head up display systems. A commoncomplication existing in many waveguide devices is banding in the outputillumination that affects its uniformity. Accordingly, variousembodiments of waveguide devices having uniform output illumination areprovided. In numerous embodiments of waveguide devices, a debandingoptic is incorporated to eliminate or mitigate banding effects.

Many embodiments are also directed to holographic waveguide technologythat can be advantageously utilized in waveguide devices. In someembodiments, the holographic waveguide technology is used for helmetmounted displays or head mounted displays (HMDs) and head up displays(HUDs). In several embodiments, holographic waveguide technology is usedin many applications, including avionics applications and consumerapplications (e.g., augmented reality glasses, etc.). In a number ofembodiments, an eye is positioned within an exit pupil or an eye box ofa display.

In many embodiments, waveguide devices provide pupil expansion in twoorthogonal directions using a single waveguide layer. Uniformity ofoutput is achieved, in accordance with various embodiments, by designingan output grating to have diffraction efficiency varying from a lowvalue near an input end of the waveguide substrate to a high value atthe furthest extremity of an output grating. In a number of embodiments,input image data is provided by a microdisplay external to a waveguideoptical substrate and coupled to the substrate by means of an inputgrating. A microdisplay, in accordance with multiple embodiments, is areflective array and illuminated via a beamsplitter. A reflected imagelight is collimated such that each pixel of the image provides aparallel beam in a unique direction.

In accordance with a number of embodiments, a waveguide device iscoupling image content into a waveguide efficiently and in such a waythat a waveguide image is free from chromatic dispersion and brightnessnon-uniformity. One way to prevent chromatic dispersion and to achievebetter collimation is to use lasers. The use of lasers, however, sufferfrom pupil banding artifacts which manifest themselves in the outputillumination causing disruption of the uniformity of the image. Bandingartifacts are able to form when a collimated pupil is replicated(expanded) in a total internal reflection (TIR) waveguide. Bandingoccurs when some light beams diffracted out of the waveguide each timethe beam interacts with the grating exhibit gaps or overlaps, leading toan illumination ripple. The degree of ripple is a function of fieldangle, waveguide thickness, and aperture thickness. As portrayed in thevarious embodiments described herein, it was found by experimentationand simulation that the effect of banding can be smoothed by dispersionwith broadband sources such as light-emitting diodes (LEDs). LEDillumination, however, is not entirely free from the banding problem,particularly for higher waveguide thickness to waveguide input-apertureratios. Moreover, LED illumination tends to result in bulky input opticsand an increase in the thickness of the waveguide device. Accordingly, anumber of embodiments of waveguide devices described herein have acompact and efficient debanding optic for homogenizing the light outputfrom holographs to prevent banding distortion.

Banding effects contribute to non-uniformity of an output illumination.As discovered in several prototype tests, a practical illumination froma waveguide device should achieve less than 20% and preferably not morethan 10% non-uniformity to provide an acceptable viewable image.Achieving low non-uniformity requires tradeoffs against other systemrequirements, particularly image brightness. The tradeoffs are difficultto define in precise terms and are very much dependent on application.Since many optical techniques for reducing non-uniformity generallyincur some light loss, output image brightness might be reduced. As thesensitivity of the human visual system to non-uniformity increases withlight level, the problem of non-uniformity becomes more acute fordisplays, such as car HUDs, which require a high luminous flux toachieve high display to background scene contrasts. Accordingly, in someembodiments, extracted light has a spatial non-uniformity less than 10%.In a number of embodiments, extracted light has a spatial non-uniformityless than 20%.

Several embodiments of the invention will now be further described withreference to the accompanying drawings. For the purposes of explainingthe various embodiments of the invention, well-known features of opticaltechnology known to those skilled in the art of optical design andvisual displays may have been omitted or simplified in order not toobscure the basic principles of the various embodiments. Description ofthe various embodiments will be presented using terminology commonlyemployed by those skilled in the art of optical design. Unless otherwisestated the term “on-axis” in relation to a ray or a beam directionrefers to propagation parallel to an axis normal to the surfaces of theoptical components described in relation to various devices. In thefollowing description, the terms light, ray, beam and direction may beused interchangeably and in association with each other to indicate thedirection of propagation of electromagnetic radiation along rectilineartrajectories. The term light and illumination may be used in relation tothe visible and infrared bands of the electromagnetic spectrum. As usedherein, the term grating may encompass a grating comprised of a set ofgratings in some embodiments.

Waveguide Devices

In accordance with a number of embodiments, a waveguide device includesat least one optical substrate, at least one light source, at least onelight coupler to couple the light from the source into the opticalsubstrate, and at least one light extractor to extract the light fromthe optical substrate to form an output illumination. Depicted in FIG.1A is an embodiment of a waveguide device. Accordingly, the waveguidedevice (100) includes at least one optical substrate (101), at least oneinput grating (102), and at least one output grating (103). The inputgrating (102), which has a maximum aperture W, couples light (ray arrows1000-1002), from a light source (104) into a total internal reflection(TIR) path (1004) within the waveguide substrate (101). The input (102)and output (103) gratings as depicted in FIG. 1A may exist in anyappropriate configuration, such as the grating configurations describedherein.

In a number of embodiments, a waveguide device includes an input imagegenerator, which further includes an input image generator having alight source, a microdisplay panel, and optics for collimating thelight. In the description of some embodiments, an input generator isreferred to as a picture generation unit (PGU). In some embodiments, asource may be configured to provide general illumination that is notmodulated with image information. In many embodiments, an input imagegenerator projects the image displayed on the microdisplay panel suchthat each display pixel is converted into a unique angular directionwithin the substrate waveguide. In various embodiments, collimationoptics include at least a lens and mirrors. In many embodiments, lensand mirrors are diffractive. In some embodiments, a light source is atleast one laser. In numerous embodiments, a light source is at least oneLED. In many embodiments, various combinations of different lightsources are used within an input image generator.

It should be understood that a number of input image generators may beused in accordance with various embodiments of the invention, such as,for example, those described in U.S. patent application Ser. No.13/869,866 entitled HOLOGRAPHIC WIDE ANGLE DISPLAY and U.S. patentapplication Ser. No. 13/844,456 entitled TRANSPARENT WAVEGUIDE DISPLAY.In many embodiments, an input image generator contains a beamsplitterfor directing light onto the microdisplay and transmitting the reflectedlight towards the waveguide. In several embodiments, a beamsplitter is agrating recorded in holographic polymer dispersed liquid crystal(HPDLC). In numerous embodiments, a beam splitter is a polarizing beamsplitter cube. In some embodiments, an input image generatorincorporates a despeckler. Any appropriate despeckler can be used invarious embodiments, such as those, for example, described in U.S. Pat.No. 8,565,560 entitled LASER ILLUMINATION DEVICE.

In a number of embodiments, a light source further incorporates one ormore lenses for modifying an illumination beam's angularcharacteristics. In many embodiments, an image source is a microdisplayor laser-based display. Several embodiments of light sources utilizeLEDs, which may provide better uniformity than laser. If laserillumination is used, the risk of illumination banding effects arehigher, but may still be eliminated or mitigated in accordance withvarious embodiments as described herein. In numerous embodiments, lightfrom a light source is polarized. In multiple embodiments, an imagesource is a liquid crystal display (LCD) microdisplay or liquid crystalon silicon (LCoS) microdisplay.

In some embodiments, an input image generator optics includes apolarizing beam splitter cube. In many embodiments, an input imagegenerator optics includes an inclined plate to which a beam splittercoating has been applied. In a number of embodiments, an input imagegenerator optics incorporates a switchable Bragg grating (SBG), whichacts as a polarization selective beam splitter. Examples of input imagegenerator optics incorporating a SBG are disclosed in U.S. patentapplication Ser. No. 13/869,866 entitled HOLOGRAPHIC WIDE ANGLE DISPLAY,and U.S. patent application Ser. No. 13/844,456 entitled TRANSPARENTWAVEGUIDE DISPLAY. In many embodiments, an input image generator opticscontains at least one of a refractive component and curved reflectingsurfaces or a diffractive optical element for controlling the numericalaperture of the illumination light. In multiple embodiments, an inputimage generator contains spectral filters for controlling the wavelengthcharacteristics of the illumination light. In several embodiments, aninput image generator optics contains apertures, masks, filter, andcoatings for controlling stray light. In some embodiments, amicrodisplay incorporates birdbath optics.

Returning to an embodiment depicted in FIG. 1A, the external source(102) provides collimated rays in an angular bandwidth (1002). Light inthe TIR path (1004) interacts with the output grating (103), extractinga portion of the light each time the TIR light satisfies the conditionfor diffraction by the grating. In the case of a Bragg gratingextraction occurs when the Bragg condition is met. For example, lightTIR ray path (1004), which corresponds to the TIR angle U, is diffractedby the output grating into output direction (1005A). It should beapparent from basic geometrical optics that a unique TIR angle isdefined by each light incidence angle at the input grating. Light isextracted, and as depicted forms three extraction beams, which are eachdepicted as flanked by two light rays (1005B & 1005C; 1006A & 1006B;1007A & 1007B). Perfectly collimated gaps (1006C & 1007C, depicted ascross-hatching) will exit between adjacent beam extracts, resulting in abanding effect. In accordance with a number of embodiments, beam gapsthat cause banding are eliminated or minimized by a number of debandingoptics as described herein. For example, a debanding optic configuresthe light such that the input grating has an effective input aperture Wthat depends on the TIR angle U.

In a multitude of embodiments, a waveguide device incorporates adebanding optic capable of shifting a pupil to configure the lightcoupled into the waveguide such that the input grating has an effectiveinput aperture which is a function of the TIR angle. The effect of thedebanding optic is that successive light extractions from the waveguideby the output grating integrate to provide a substantially flatillumination profile for any light incidence angle at the input grating.In some embodiments, a debanding optic is implemented by combiningvarious types of optical beam-modifying layers, including (but notlimited to) gratings, partially reflecting films, liquid crystalalignment layers, isotropic refractive layers and gradient index (GRIN)structures. It should be understood, that the term “beam-modifying”refers to the variation of amplitude, polarization, phase, and wavefrontdisplacement in 3D space as a function of incidence light angle. In eachcase, beam-modifying layers, in accordance with several embodiments,provide an effective aperture that gives uniform extraction across theoutput grating for any light incidence angle at the input grating. Inmany embodiments, beam-modifying layers are used in conjunction with ameans for controlling the numerical aperture of the input light as afunction of input angle. In some embodiments, beam-modifying layers areused in conjunction with techniques for providing wavelength diversity.

FIG. 1B provides a chart illustrating the effect of pupil shiftingoptics on the light output (labeled I) from the waveguide along aprincipal propagation direction labeled as Z (referring to thecoordinate system shown in FIG. 1A). Intensity profiles (1008A-1008C)for three successive extractions corresponding to an input lightdirection are shown. The shape of the intensity profiles is controlledby the prescriptions of beam-modifying layers. In a number ofembodiments, intensity profiles are integrated to provide asubstantially flat intensity profile. For example, the intensityprofiles (1008A-1008C) are integrated into a flat profile (1009).

Input Couplers and Extractors Utilized in Waveguide Devices

Waveguide devices are currently of interest in a range of display andsensor applications. Although much of the earlier work on devices hasbeen directed at reflection holograms, transmission, devices are provingto be much more versatile as optical system building blocks.Accordingly, a number of embodiments are directed to the use of gratingsin waveguide devices, which may be used for input or output of pupil. Inmany embodiments, an input grating is a type of input coupler of lightto couple light from a source into a waveguide. In numerous embodiments,an output grating is a type of light extractor of light to extract lightfrom a waveguide to form an output illumination. In several embodiments,waveguide devices utilize a Bragg grating (also referred to as a volumegrating). Bragg gratings have high efficiency with little light beingdiffracted into higher orders. The relative amount of light in thediffracted and zero order can be varied by controlling the refractiveindex modulation of the grating, a property that is used to make lossywaveguide gratings for extracting light over a large pupil.

As used herein, the term grating may encompass a grating comprised of aset of gratings in some embodiments. For example, in some embodiments aninput grating and/or output grating separately comprise two or moregratings multiplexed into a single layer. It is well established in theliterature of holography that more than one holographic prescription canbe recorded into a single holographic layer. Methods for recording suchmultiplexed holograms are well known to those skilled in the art. Insome embodiments, an input grating and/or output grating separatelycomprise two overlapping gratings layers that are in contact orvertically separated by one or more thin optical substrate. In manyembodiments, grating layers are sandwiched between flanking glass orplastic substrates. In several embodiments, two or more gratings layersmay form a stack within which total internal reflection occurs at theouter substrate and air interfaces. In a number of embodiments, awaveguide device may comprise just one grating layer. In someembodiments, electrodes are applied to faces of substrates to switchgratings between diffracting and clear states. A stack, in accordancewith numerous embodiments, further includes additional layers such asbeam splitting coatings and environmental protection layers.

In numerous embodiments, a grating layer is broken up into separatelayers. A number of layers are laminated together into a singlewaveguide substrate, in accordance with various embodiments. In someembodiments, a grating layer is made of several pieces including aninput coupler, a fold grating, and an output grating (or portionsthereof) that are laminated together to form a single substratewaveguide. In many embodiments, pieces of waveguide devices areseparated by optical glue or other transparent material of refractiveindex matching that of the pieces. In a multitude of embodiments, agrating layer is formed via a cell making process by creating cells ofthe desired grating thickness and vacuum filling each cell withSwitchable Bragg Grating (SBG) material for each of an input coupler, afold grating, and an output grating. In a number of embodiments, a cellis formed by positioning multiple plates of glass with gaps between theplates of glass that define the desired grating thickness for an inputcoupler, a fold grating, and an output grating. In many embodiments, onecell may be made with multiple apertures such that the separateapertures are filled with different pockets of SBG material. Anyintervening spaces, according to various embodiments, are separated by aseparating material (e.g., glue, oil, etc.) to define separate areas. Inmultiple embodiments, SBG material is spin-coated onto a substrate andthen covered by a second substrate after curing of the material. Byusing a fold grating, a waveguide display advantageously requires fewerlayers than previous systems and methods of displaying informationaccording to some embodiments. In addition, by using a fold grating,light can travel by total internal refection within the waveguide in asingle rectangular prism defined by the waveguide outer surfaces whileachieving dual pupil expansion. In many embodiments, an input couplerand gratings can be created by interfering two waves of light at anangle within the substrate to create a holographic wave front, therebycreating light and dark fringes that are set in the waveguide substrateat a desired angle. In numerous embodiments, a grating in a given layeris recorded in stepwise fashion by scanning or stepping the recordinglaser beams across the grating area. In some embodiments, gratings arerecorded using mastering and contact copying process currently used inthe holographic printing industry.

Input and output gratings, in accordance with many embodiments, aredesigned to have common surface grating pitch. In some embodiments, aninput grating combines a plurality of gratings orientated such that eachgrating diffracts a polarization of the incident unpolarized light intoa waveguide path. In many embodiments, an output grating combines aplurality of gratings orientated such that the light from the waveguidepaths is combined and coupled out of the waveguide as unpolarized light.Each grating is characterized by at least one grating vector (orK-vector) in 3D space, which in the case of a Bragg grating is definedas the vector normal to the Bragg fringes. A grating vector determinesan optical efficiency for a given range of input and diffracted angles.

One important class of gratings is known as Switchable Bragg Gratings(SBG), which are utilized in various waveguide devices in accordancewith many embodiments. Typically, a holographic polymer dispersed liquidcrystal (HPDLC) is used in SBGs. In many embodiments, HPDLC includes amixture liquid crystal (LC), monomers, photoinitiator dyes, andcoinitiators. Often, a mixture also includes a surfactant. The patentand scientific literature contains many examples of material systems andprocesses that may be used to fabricate SBGs. Two fundamental patentsare: U.S. Pat. No. 5,942,157 by Sutherland, and U.S. Pat. No. 5,751,452by Tanaka et al. Both filings describe monomer and liquid crystalmaterial combinations suitable for fabricating SBG devices. One of theknown attributes of transmission SBGs is that the LC molecules tend toalign normal to the grating fringe planes. The effect of the LC moleculealignment is that transmission SBGs efficiently diffract P polarizedlight (i.e., light with the polarization vector in the plane ofincidence) but have nearly zero diffraction efficiency for S polarizedlight (i.e., light with the polarization vector normal to the plane ofincidence). Transmission SBGs may not be used at near-grazing incidenceas the diffraction efficiency of any grating for P polarization falls tozero when the included angle between the incident and reflected light issmall.

In a number of embodiments, SBGs are fabricated by first placing a thinfilm of a mixture of photopolymerizable monomers and liquid crystalmaterial between parallel glass plates. One or both glass plates supportelectrodes for applying an electric field across the film. In numerousembodiments, electrodes are made at least in part by transparent indiumtin oxide films. A volume phase grating can then be recorded byilluminating liquid crystal material (often referred to as the syrup)with two mutually coherent laser beams, which interfere to form aslanted fringe grating structure, in accordance with multipleembodiments. During a recording process, monomers polymerize and themixture undergoes a phase separation, creating regions densely populatedby liquid crystal micro-droplets, interspersed with regions of clearpolymer, resulting in a HPDLC. In accordance with several embodiments,alternating liquid crystal-rich and liquid crystal-depleted regions ofan HPDLC device form fringe planes of a grating. A resulting volumephase grating can exhibit very high diffraction efficiency, which may becontrolled, in accordance with various embodiments, by the magnitude ofthe electric field applied across the film. When an electric field isapplied to a grating via transparent electrodes, a natural orientationof the LC droplets is changed, reducing the refractive index modulationof the fringes and dropping a hologram diffraction efficiency to verylow levels. Typically, SBG Elements are switched clear in 30 μs, with alonger relaxation time to switch ON. Note that the diffractionefficiency of a device can be adjusted, in accordance with manyembodiments, by means of applied voltage over a continuous range. Adevice exhibits near 100% efficiency when no voltage is applied andnear-zero efficiency when a sufficiently high voltage is applied. Incertain embodiments, of HPDLC devices, magnetic fields may be used tocontrol the LC orientation. In certain embodiments of HPDLC devices,phase separation of LC material from polymer may be accomplished to sucha degree that no discernible droplet structure results. In a number ofembodiments, a SBG is also used as a passive grating, which may providea benefit of a uniquely high refractive index modulation.

According to numerous embodiments, SBGs are used to provide transmissionor reflection gratings for free space applications. Various embodimentsof SBGs are implemented as waveguide devices in which the HPDLC formseither the waveguide core or an evanescently coupled layer in proximityto the waveguide. In many embodiments, parallel glass plates used toform the HPDLC cell provide a total internal reflection (TIR) lightguiding structure. Light is coupled out of a SBG, in accordance withseveral embodiments, when a switchable grating diffracts light at anangle beyond the TIR condition.

In many embodiments of waveguide devices based on SBGs, gratings areformed in a single layer sandwiched by transparent substrates. In anumber of embodiments, a waveguide is just one grating layer. In variousembodiments that incorporate switchable gratings, transparent electrodesare applied to opposing surfaces of the substrate layers sandwiching theswitchable grating. In some embodiments, cell substrates are fabricatedfrom glass. An exemplary glass substrate is standard Corning Willowglass substrate (index 1.51), which is available in thicknesses down to50 microns. In a number of embodiments, cell substrates are opticalplastics.

It should be understood that Bragg gratings could also be recorded inother materials. In several embodiments, SBGs are recorded in a uniformmodulation material, such as POLICRYPS or POLIPHEM having a matrix ofsolid liquid crystals dispersed in a liquid polymer. In multipleembodiments, SBGs are non-switchable (i.e., passive). Non-switchableSBGs may have the advantage over conventional holographic photopolymermaterials of being capable of providing high refractive index modulationdue to its liquid crystal component. Exemplary uniform modulation liquidcrystal-polymer material systems are disclosed in United State PatentApplication Publication No. US2007/0019152 by Caputo et al and PCTApplication No.: PCT/EP2005/006950 by Stumpe et al. both of which areincorporated herein by reference in their entireties. Uniform modulationgratings are characterized by high refractive index modulation (andhence high diffraction efficiency) and low scatter. In many embodiments,at least one grating is a surface relief grating. In some embodiments atleast one grating is a thin (or Raman-Nath) hologram.

In multiple embodiments, gratings are recorded in a reverse mode HPDLCmaterial. Reverse mode HPDLC differs from conventional HPDLC in that thegrating is passive when no electric field is applied and becomesdiffractive in the presence of an electric field. Reverse mode HPDLC maybe based on any of the recipes and processes disclosed in PCTApplication No.: PCT/GB2012/000680, entitled IMPROVEMENTS TO HOLOGRAPHICPOLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES. A grating may berecorded in any of the above material systems, in accordance of variousembodiments, but used in a passive (non-switchable) mode. Thefabrication process is identical to that used for switchable gratings,but with an electrode coating stage being omitted. LC polymer materialsystems are highly desirable in view of their high index modulation. Insome embodiments, gratings are recorded in HPDLC but are not switchable.

In some embodiments, a grating encodes optical power for adjusting thecollimation of the output. In many embodiments, an output image is atinfinity. In numerous embodiments, an output image may be formed atdistances of several meters from an eye box.

In several embodiments, an input grating may be replaced by another typeof input coupler. In particular embodiments, an input grating isreplaced with a prism or reflective surface. In a number of embodiments,an input coupler can be a holographic grating, such as a switchable ornon-switchable SBG grating. The input coupler is configured to receivecollimated light from a display source and to cause the light to travelwithin the waveguide via total internal reflection between the firstsurface and second surfaces.

It is well established in the literature of holography that more thanone holographic prescriptions can be recorded into a single holographiclayer. Methods for recording such multiplexed holograms are well knownto those skilled in the art. In some embodiments, at least one of aninput or output grating combines two or more angular diffractionprescriptions to expand the angular bandwidth. In many embodiments, atleast one of the input or output gratings combines two or more spectraldiffraction prescriptions to expand the spectral bandwidth. In numerousembodiments, a color multiplexed grating is used to diffract two or moreprimary colors.

Many embodiments, as described herein, are operated in monochrome. Acolor waveguide, however according to various embodiments of theinvention, includes a stack of monochrome waveguides. In a number ofembodiments, a waveguide device uses red, green and blue waveguidelayers. In several embodiments, a waveguide device uses red andblue/green layers. In some embodiments, gratings are all passive, thatis, non-switchable. In multiple embodiments, at least one grating isswitchable. In a number of embodiments, input gratings in each layer areswitchable to avoid color crosstalk between waveguide layers. In someembodiments, color crosstalk is avoided by disposing dichroic filtersbetween the input grating regions of the red and blue and the blue andgreen waveguides.

In a number of embodiments, light is characterized by a wavelengthbandwidth. In many embodiments, a waveguide device is capable ofdiversifying the wavelength bandwidth of light. In accordance to variousembodiments, Bragg gratings, which are inherently spectral bandwidthlimited devices, are most efficiently utilized with narrow band sourcessuch as LEDs and lasers. A Bragg grating, in accordance to manyembodiments, diffracts two different wavelength bands with highefficiency when the grating prescription and the incident light rayangles satisfy the Bragg equation. Full color waveguides, in accordanceto multiple embodiments, utilize separate specific wavelength layers,such as, red, green and blue diffracting waveguide layers. Two-layersolutions in which one layer diffracts two of the three primary colorsare used in numerous embodiments. In many embodiments, a naturalspectral bandwidth of a Bragg grating is adequate for minimizing colorcross talk. For tighter control of color crosstalk, however, additionalcomponents such as dichroic filters and narrow band filters integratedbetween waveguide layers and, typically, overlapping the input gratingsmay be used.

Debanding Optics

In numerous embodiments, a debanding optic is an effective inputaperture such that when the optical substrate has a thickness D, theinput aperture is configured to provide a TIR angle U in the opticalsubstrate, and the angle U is calculated by 2D tan (U). Provided in FIG.2 is an embodiment of a waveguide device (110) incorporating a debandingoptic in a form of a waveguide that includes a waveguide substrate (111)and a TIR (1012) such that a condition of zero banding exists. In manyembodiments, a condition of zero banding, that is no gaps betweensuccessive light extractions along the TIR ray path, occurs when theeffective input aperture for a TIR angle U and a waveguide substratethickness D is given by 2D tan (U).

In some embodiments, a debanding optic provides spatial variation of thelight along a TIR path of at least one of diffraction efficiency,optical transmission, polarization or birefringence. A typical spatialvariation (120) is provided in the chart FIG. 3 by the curve (1020)where the Y-axis refers to the value of any of the above parameters(e.g., diffraction efficiency) and X-axis is a beam propagationdirection within the waveguide. In a number of embodiments, a spatialvariation is in two dimensions (in the plane of the waveguide).

In some embodiments, a debanding optic is at least one gratingconfigured to have multiple gratings, such that each grating provides asmall pupil shift to eliminate or mitigate banding. In many embodiments,a stack of multiple gratings achieves a small pupil shift whenseparations between the gratings within the stack are designed toprovide a pupil shift for each angle. In a number of embodiments,gratings capable of a pupil shift are separated by transparentsubstrates. In several embodiments, gratings capable of a pupil shiftare passive. Alternatively, in some embodiments, gratings are switchedon when a voltage is applied. In some embodiments, multiple gratingsarranged to have lateral relative displacements provides a pupil shift.In numerous embodiments, multiple gratings are configured in atwo-dimensional array with different sub arrays of grating elementsbeing switched in to their diffraction states according to an incidenceangle. In some embodiments, gratings are configured as stacks of arrays.In various embodiments, separate gratings are provided for differentwavelength bands. In a number of embodiments, a grating is multiplexed.

In many embodiments, gratings have grating parameters that vary acrossthe principal plane of a waveguide. In some embodiments, a diffractionefficiency is varied to control the amount of light diffracted versusthe amount of light transmitted down the waveguide as zero order light,thereby enabling the uniformity of light extracted from the waveguide tobe fine-tuned. In several embodiments, K-vectors of at least one gratinghas rolled K-vectors which have directions optimized to fine tune theuniformity of light extracted from the waveguide. In variousembodiments, an index modulation of gratings is varied to fine tune theuniformity of light extracted from the waveguide. In numerousembodiments, a thickness of the gratings is varied to fine tune theuniformity of light extracted from the waveguide.

In a number of embodiments, a debanding optic is at least one gratingconfigured as a stacked switchable grating that turns on when a voltageis applied, shifting pupil to eliminate or mitigate banding effects.Depicted in FIG. 4 is an embodiment of a waveguide device (130) with anoptical substrate (131) having stacked switchable input gratings (132A &1326) and a non-switchable output grating (133). A voltage supply (134)is coupled to the input gratings (132A & 1326) by an electricalconnection (135A & 1356) to switch on the input gratings (132A & 132B)to provide pupil shift. Depicted in FIG. 5 is an embodiment of awaveguide device (141) having a non-switchable input grating and aswitchable output gating having stacked grating layers (143A & 143B). Avoltage supply (144) is coupled to the output gratings (143A & 143B) byan electrical connection (145A & 145B) to switch on the output gratings(143A & 143B) to provide a pupil shift. In various embodiments, a thinsubstrate layer exits between stacked gratings to provide at least someseparation.

In some embodiments, a debanding optic is at least one gratingconfigured as an array of switchable grating elements that can turn on aspecific element when a voltage is applied, shifting pupil to eliminateor mitigate banding effects. Depicted in FIG. 6A is an embodiment of awaveguide device (150) having an optical substrate (151) that containsinput gratings (152A & 152B) each having a plurality of grating elements(153A-156A & 153B-156B) and an output grating (157). The waveguidedevice further includes a voltage supply (158) coupled to each inputgrating (152A & 152B) by an electrical connection (159A & 159B)configured to individually switch on each element (e.g., 156A & 156B) toshift pupil. Although not depicted, it should be understood that avoltage supply can be connected to each and every element to create anarray of switchable elements. Furthermore, although FIG. 6A only depictsan input grating configured to be an array, it should be understood thatan output grating can also be an array of elements, each elementconfigured to be switchable, in accordance with a number of embodimentsof the invention.

In various embodiments, a grating has a plurality of rolled K-vectors. AK-vector is a vector aligned normal to the grating planes (or fringes)which determines the optical efficiency for a given range of input anddiffracted angles. Rolling K-vectors, in accordance with a number ofembodiments, allows an angular bandwidth of a grating to be expandedwithout the need to increase the waveguide thickness. Depicted in FIG.6B is an embodiment of a grating (152C) having four rolled K-vectors(K₁-K₄). In a number of embodiments, a grating is configured as atwo-dimensional array of switchable elements. For example, depicted inFIG. 7, a grating is configured as a two-dimensional array (160) ofswitchable elements (e.g., 161).

In numerous embodiments, a debanding optic is at least one gratingconfigured to be a plurality of passive grating layers configured toshift pupil to eliminate or mitigate banding effects. When a waveguidedevice incorporates multiple passive grating layers, in accordance withvarious embodiments, the basic architecture is similar to some of theembodiments that incorporate active grating layers (e.g., see FIGS. 4 &5) but without a voltage supply. In some embodiments, it is advantageousto use SBGs in non-switchable mode to take advantage of the higher indexmodulation afforded by a number of liquid crystal polymer materialsystems. In many embodiments, a debanding optic is at least onemultiplexed grating configured to shift pupil to eliminate or mitigatebanding effects.

In some embodiments, a waveguide device includes a fold grating forproviding exit pupil expansion. It should be understood that variousfold gratings may be used in accordance with various embodiments of theinvention. Examples of various fold gratings that may be used in amultitude of embodiments are disclosed in PCT Application No.PCT/GB2016000181 entitled WAVEGUIDE DISPLAY or as described in otherreferences cited herein. A fold grating, in accordance of severalembodiments, incorporates multiple gratings for pupil shifting toeliminate or mitigate banding effects, with each grating providing asmall pupil shift.

In many embodiments, a debanding optic is one or more index layersdisposed within an optical substrate such that the one or more indexlayers influences the light ray paths within the optical substrate as afunction of at least one of ray angle or ray position, shifting pupil tomitigate banding effects. In some embodiments, at least one index layeris a GRIN medium. It should be understood that various GRIN mediums maybe used in accordance with various embodiments of the invention, such asthe examples of various GRIN mediums that are described in U.S.Provisional Patent Application No. 62/123,282 entitled NEAR EYE DISPLAYUSING GRADIENT INDEX OPTICS and U.S. Provisional Patent Application No.62/124,550 entitled WAVEGUIDE DISPLAY USING GRADIENT INDEX OPTICS.

In a number of embodiments, a debanding optic is one or more indexlayers disposed adjacent to at least one reflecting surface of an edgeof an optical substrate such that the one or more layers are configuredto provide pupil shifting to eliminate or mitigate banding effects.Depicted in FIG. 8 is an embodiment of a waveguide device (170) havingan optical substrate (171) that contains an input grating (172) and anoutput grating (173) with one or more stacked index layers (174)disposed adjacent an upper reflecting surface of the waveguide such thatthe one or more index layers provide pupil shifting. In manyembodiments, a debanding optic is one or more index layers disposedwithin an optical substrate such that the one or more layers areconfigured to provide pupil shifting to eliminate or mitigate bandingeffects. For example, depicted in FIG. 9 is an embodiment of a waveguidedevice (180) having an optical substrate (181) that contains an inputgrating (182) and an output grating (183) with one or more stacked indexlayers (184) disposed within the optical substrate (181) such that theone or more layers (184) are configured to provide pupil shifting. Insome embodiments, a waveguide device incorporates a debanding optic thatincludes one or more index layers disposed within an optical substrateand one or more index layers also disposed adjacent to at least onereflecting surface of the optical substrate.

In several embodiments, a debanding optic is an input grating having aleading edge able to couple incident light such that a uniquedisplacement of a ray bundle of the light relative to the leading edgeof the input grating is provided by the input grating for any givenincident light direction, shifting pupil to eliminate or mitigatebanding effects. Depicted in FIG. 10 is a detail of an embodiment of awaveguide device (190) having an optical substrate (191) that containsan input grating (192) with a leading edge (193). Collimated input raypaths for two different input angles (1090 & 1091) and the correspondingdiffracted rays (1092 & 1093) are depicted. Separations of edges of thetwo ray sets from the leading edge of the input gratings (1094 & 1095)are depicted. In some embodiments, a displacement of light relative toan edge of an input grating of a ray bundle results in a portion of thebeam to fall outside the input grating apertures and therefore not beingdiffracted into a TIR path inside an optical substrate, depending on thefield angle of the incoming light. A suitable absorbing film trapsnon-diffracted light, in accordance with various embodiments. Hence abeam width can be tailored to meet a debanding condition, when a TIRangle U and a waveguide substrate thickness D is given by 2D tan (U), aswas described in greater detail in relation to FIG. 2. An example ofsuch an embodiment will be discussed in greater detail in a subsequentsection (see FIG. 20).

In many embodiments, a debanding optic is an input grating configured tohave a variation of diffraction efficiencies such that a plurality ofcollimated incident ray paths of the incident light is diffracted intodifferent TIR ray paths, as determined by a ray path input angle, suchthat a projected pupil is capable of forming at a unique location withinthe optical substrate for each of the plurality of collimated incidentray paths to eliminate or mitigate banding effects. Depicted in FIG. 11is a detail of an embodiment of a waveguide device (200) having anoptical substrate (201) that contains an input grating (202). Collimatedinput ray paths for two different input angles (1100 &1101) arediffracted by the input grating (202) such that the diffracted rays(1102 & 1103) each follow a TIR path down the optical substrate (201).Each TIR ray path (1104 & 1105) forms a projected pupil (1106 & 1107) ina unique location, based on the incident angle, and such that bandingeffects are eliminated and/or mitigated.

In some embodiments, a variation of diffraction efficiencies variesalong a principal waveguide direction to provide, at least in part,pupil shift to eliminate or mitigate banding effects. In manyembodiments, a variation of diffraction efficiencies varies in twodimensions over the aperture of the input grating.

In some embodiments, a debanding optic is a partially reflecting layerdisposed within an optical substrate such that the partially reflectinglayer separates incident light into transmitted and reflected light,shifting pupil to eliminate or mitigate banding effects. Depicted inFIG. 12 is a detail of an embodiment of a waveguide device (210) havingan optical substrate (211) that contains a partially reflecting layer(212), capable of separating incident light (1110) into transmittedlight (1000) and reflected light (1111). Transmitted and reflected light(1000 & 1111) each follow a TIR path along a waveguide substrate (211),resulting in a pupil shift to eliminate or mitigate banding effects.

In numerous embodiments, a debanding optic is a polarization modifyinglayer disposed within an optical substrate such that the polarizationmodifying layer separates incident light into transmitted and reflectedlight, shifting pupil to eliminate or mitigate banding effects. Forexample, FIG. 13 provides a detail of an embodiment of a waveguidedevice (220) having an optical substrate (221) that contains a partiallyreflecting polarization modifying layer (222), which separates incidentlight (1120) having a polarization vector (1123) into transmitted light(1121) having a polarization vector (1124), resulting from the retardingeffect of a polarization modifying layer (222), and reflected light(1122). Transmitted (1121) and reflected light (1122) follow TIR pathsdown the optical substrate (221) resulting in a pupil shift to eliminateor mitigate banding effects. In some embodiments, a polarizationmodifying layer is formed by stretching a polymeric material in at leastone dimension. In particular embodiments, a polarization modifying layeris a polymeric material, such as birefringent polyester,polymethylmethacrylate (PMMA), or poly-ethylene terephthalate (PET).Polymeric materials may be used in a single layer or two or more may becombined in a stack.

In many embodiments, a debanding optic is at least one gratingconfigured to provide at least two separate waveguide paths which cancelnon-uniformity of light of the extracted light for any incidence lightangle, eliminating or mitigating banding effects. In severalembodiments, a debanding optic includes at least one grating havingcrossed slant gratings used in conjunction with at least one foldgrating exit pupil expander configured to provide a pupil shift toeliminate or mitigate banding effects. Depicted in FIG. 14 is anembodiment of a waveguide device (230) having an optical substrate (231)coupled to an input image generator (232). The optical substrate (231)contains an input grating (233) with crossed slant gratings (233A &233B), a first fold grating exit pupil expander (234) containing agrating (235), a second fold grating exit pupil expander (236)containing a grating (237), and an output grating (238) with crossedslant gratings (238A & 238B). The input grating (233) receives lightfrom the input image generator (232) in a direction (1130), such thatthe direction is normal to the surface of the input grating (233). Innumerous embodiments, crossed gratings in a grating have a relativeangle of approximately ninety degrees in the plane of an opticalsubstrate. It should be noted, however, other angles may be used inpractice and still fall within various embodiments of the invention.

In several embodiments, a debanding optic is a system of gratings, suchthat an input grating and an output grating each combine crossedgratings with peak diffraction efficiency for orthogonal polarizationsstates. In some embodiments, polarization states created by input andoutput gratings are S-polarized and P-polarized. In a number ofembodiments, polarization states created by input and output gratingsare opposing senses of circular polarization. Several embodimentsutilize gratings recorded in liquid crystal polymer systems, such asSBGs, which may have an advantage owing to their inherent birefringenceand exhibiting strong polarization selectivity. It should be noted,however, that other grating technologies that can be configured toprovide unique polarization states may be used and still fall withinvarious embodiments of the invention.

Returning to FIG. 14, a first polarization component of the input lightincident on the input grating (233) along a direction (1130) is directedby a grating (233B) into a TIR path along a direction (1131) and asecond polarization component is directed by a second grating (233A)into a second TIR path along a direction (1132). Light traveling alongthe TIR paths (1131 &1132) is expanded in the plane of the opticalsubstrate (231) by fold gratings (234 & 236) and diffracted into secondTIR paths (1133 & 1134) towards an output grating (238). Crossed slants(238A & 238B) of the output grating (238) diffract light from the secondTIR paths (1133 & 1134) into a uniform output path (1135) such thatbanding effects are eliminated or mitigated. In some embodiments, agrating prescription is designed to provide dual interaction of guidedlight with the grating, which may enhance a fold grating angularbandwidth. A number of embodiments of dual interaction fold gratings canbe used, such as the gratings described in U.S. patent application Ser.No. 14/620,969 entitled WAVEGUIDE GRATING DEVICE.

In several embodiments, a debanding optic is an optical component withina microdisplay that provides variable effective numerical apertures (NA)capable of being spatially varied along at least one direction to shiftpupil to eliminate or mitigate banding effects. Depicted in FIG. 15 isan embodiment an input image generator (240) designed to have anumerical aperture (NA) variation ranging from high NA on one side ofthe microdisplay (241) panel varying smoothly to a low NA at the otherside to provide a pupil shift. For the purposes of explanation, a NA inrelation to a microdisplay is defined herein as being proportional tothe sine of the maximum angle of the image ray cone from a point on themicrodisplay surface with respect to an axis normal to the microdisplay.As shown in FIG. 15, the NA of the microdisplay (241) is spatiallyvaried by an optical component (242) which causes the NA to vary acrossat least one principal dimension of the microdisplay as indicated by theextending light rays (1140-1142). It should be understood that anoptical component used to vary a NA may be any appropriate opticalcomponent, such as any of the optical components described in PCTApplication No.: PCT/GB2016000181 entitled WAVEGUIDE DISPLAY. Inmultiple embodiments, a microelectromechanical systems (MEMS) array isused to spatially vary the (NA) across a microdisplay display panel. Innumerous embodiment, a MEMs array spatially varies the NA of lightreflected from a microdisplay panel. In many embodiments, a MEMS arrayutilizes technology used in data projectors.

In several embodiments, a microdisplay is a reflective device. In someembodiments, a microdisplay is a transmission device, such as, forexample, a transmission liquid crystal on silicon (LCoS) device. In manyembodiments, an input image generator has a transmission microdisplaypanel with a backlight and a variable NA component. When a backlight isemployed, in accordance with various embodiments, the illuminated lighttypically has a uniform NA across, illuminating a back surface of amicrodisplay, which is propagated through a variable NA component andconverted into an output image modulated light with NA angles varyingalong a principal axis of the microdisplay.

In a number of embodiments, an emissive display is employed in amicrodisplay. Examples of emissive displays for use within amicrodisplay include, but not limited to, LED arrays and light emittingpolymers arrays. In some embodiments, an input image generatorincorporates an emissive microdisplay and a spatially-varying NAcomponent. Light from a microdisplay employing an emissive display, inaccordance with various embodiments, typically has a uniform NA acrossthe emitting surface of the display, illuminates the spatially-varyingNA component and is converted into an output image modulated light withNA angles varying across the display aperture.

In many embodiments, a debanding optic is a plurality of grating layerswithin at least one grating such that the plurality of grating layers isconfigured to smear out any fixed pattern noise resulting in pupil shiftto eliminate or mitigate banding effects. Depicted in FIG. 16A is anembodiment of a waveguide device (250) having a picture generation unit(PGU) (251), optically coupled to an optical substrate (252) thatextracts light via an output grating (253). The optical substrate (252)contains stacked input gratings (254 & 255) and a fold grating that isnot illustrated. Input light (1150) from the PGU (251) is coupled intothe waveguide substrate (252) by the input gratings (254 & 255),smearing out any fixed pattern noise, and diffracted into TIR paths(1151), and then diffracted into extracted light (1152) by the outputgrating (253) resulting in a pupil shift to eliminate or mitigatebanding effects. In some embodiments, multiple gratings are combinedinto a multiplexed grating.

In several embodiments, a debanding optic is the input gratingconfigured as an array of selectively switchable elements such thatconfiguring the input grating as a switching grating array providespupil switching in vertical and horizontal directions to shift pupil toeliminate or mitigate banding effects. In many embodiments, individualgrating elements are designed to diffract light incident in predefinedinput beam angular ranges into corresponding TIR angular ranges.Depicted in FIG. 16B is an embodiment of a waveguide device (260) havinga PGU (261), optically coupled to an optical substrate (262) thatextracts light via an output grating (253). The optical substrate (262)contains a switchable input grating array (264) of selectivelyswitchable elements (265). Input light (1160) is coupled into theoptical substrate (262) by the input grating (264), which provides pupilshift in vertical and horizontal directions that is diffracted into TIRpaths (1161), and then diffracted into extracted light (1162) by theoutput grating (263) with banding effects eliminated or mitigated.

In numerous embodiments, a debanding optic is a plurality of refractiveindex layers that provide spatial variation along each TIR path of atleast one of diffraction efficiency, optical transmission, polarizationand birefringence to influence ray paths within a waveguide substrate asa function of at least one of ray angle or ray position within thesubstrate, resulting in shift of pupil to eliminate or mitigate bandingeffects. In several embodiments, a plurality of refractive index layersincorporates adhesives of different indices, especially to influencehigh angle reflections. In some embodiments, a plurality of refractiveindex layers incorporate layers, such as alignment layers, isotropicrefractive layers, GRIN structures, antireflection layers, partiallyreflecting layer, or birefringent stretched polymer layers. Depicted inFIG. 16C is an embodiment of a waveguide device (270) having a PGU (271)optically coupled to an optical substrate (272) that extracts light viaan output grating (273). The optical substrate (272) contains an inputgrating (274) and at least one refractive index layer (275). Input light(1170) is coupled into the optical substrate (272) by the input grating(275) and diffracted into TIR paths (1171) that pass through therefractive index layer (275) causing spatial variation, and thendiffracted into extracted light (1172) by the output grating (273),resulting in a pupil shift to eliminate or mitigate banding effects.

In some embodiments, a debanding optic is a microdisplay projectingspatially varied NAs that shift pupil to eliminate or mitigate bandingeffects. In several embodiments, NA can be varied in two orthogonaldirections. Depicted in FIG. 16D is an embodiment of a waveguide device(280) having a PGU (281) optically coupled to an optical substrate (282)that extracts light via an output grating (283). The optical substrate(282) contains an input grating (285). Input light (1180) is coupledinto the optical substrate (282) by the input grating (285) anddiffracted into TIR paths (1181), and then diffracted into extractedlight (1182) by the output grating (283). The PGU (281) has amicrodisplay (286) overlaid by an NA modification layer (287) capable ofspatially varying NA and modifying the light into varying beam profiles(1184-1186), resulting in pupil shift to eliminate or mitigate bandingeffects. In accordance with various embodiments, a PGU also incorporatesother components, such as a projection lens and/or beamsplitter, forexample.

In many embodiments, a debanding optic is a tilted microdisplayconfigured to project a tilted, rectangular exit pupil such that thecross section of the exit pupil varies with a field angle, such thatbanding effects are eliminated or mitigated. In a number of embodiments,an exit pupil changes position on an input grating. This technique, inaccordance with various embodiments, can be used to address banding inone beam expansion axis. Depicted in FIG. 16E is an embodiment of awaveguide device (290) having a PGU (291) optically coupled to anoptical substrate (292) which extracts light via an output grating(293). Input light (1190) emerging from the tilted PGU exit pupil (295)is coupled into the waveguide via an input grating (294) and diffractedinto TIR paths (1191), and then diffracted into extracted light (1192)by the output grating (293), eliminating or mitigating banding effects.

In several embodiments, a debanding optic is a tilted microdisplayconfigured to angle light rays to form various projected pupils atdifferent positions along an optical substrate for each direction ofincident light, such that banding effects are mitigated along oneexpansion axis. Depicted in FIG. 16F is an embodiment of a waveguidedevice (300) having a PGU (301) optically coupled to an opticalsubstrate (302), which extracts light via an output grating (303). Inputlight (1200) emerging from the tilted PGU exit pupil (305) is coupledinto the waveguide by an input grating (304) and diffracted into TIRpaths (1201). The guided light forms beam angle-dependent projectedpupils (1203-1205) at different positions along the substrate (302) foreach direction of incident light, and then diffracted into extractedlight (1202) by the output grating (303), eliminating or mitigatingbanding effects.

In numerous embodiments, a debanding optic is a prism coupled to anoptical substrate, such that a linear relationship between the angles ofan exit pupil from a light source and the TIR angles in the opticalsubstrate result in no gaps between successive light extractions alongthe TIR ray path, which occurs when the TIR path angle is U as definedby 2D tan (U). In many embodiments, an input grating is replaced with acoupling prism. In several embodiments, input light is provided througha tilted PGU pupil. By selecting a prism angle and cooperative PGU pupiltilt, in accordance with various embodiments, it is possible to achievean approximately linear relationship between the angles out of the PGUexit pupil and the TIR angles in the waveguide while meeting a debandingcondition when the effective input aperture for a TIR angle U and awaveguide substrate thickness D is given by 2D tan (U), over the entirefield of view range. Depicted in FIG. 16 G is an embodiment of awaveguide device (310) having a PGU (311) optically coupled to anoptical substrate (312), which extracts light via an output grating(313). Input light (1210) emerging from a tilted PGU exit pupil (315) iscoupled into the optical substrate (312) by a prism (314) resulting inTIR paths (1211) and then diffracted into extracted light (1192) by theoutput grating (293), eliminating or mitigating banding effects. In someembodiments, color dispersion due to the prism is compensated by adiffractive surface. In many embodiments, a prism coupler has refractingsurface apertures designed to shape the light as a function of angle.Light at the edges of the beam that is not transmitted through the prisminto the waveguide is eliminated from the main light path by baffling orlight absorbing coatings, in accordance with a number of embodiments.

In some embodiments, a debanding optic is a light-absorbing filmadjacent to the edges of an optical substrate such that portions ofincident light, that would otherwise give rise to banding, are removed,eliminating or mitigating banding effects. Depicted in FIG. 16H is anembodiment of a waveguide device (320) designed for beam shifting alongone axis of beam expansion. The waveguide device has a PGU (321) coupledto a waveguide (322) containing an output grating (323) and an inputgrating (324), a substrate (325) having a light-absorbing film (326)applied to one of its edges, a substrate (327) having a light-absorbingfilm (328) applied to one its edges, the substrates (325 & 327)sandwiching the portion of the waveguide (322) that contains the inputgrating. The input ray at the upper limit of the input beam (1221) isdiffracted by the input grating (324) into a TIR path (1223) andabsorbed by the light-absorbing film (326) applied to the substrate(325), eliminating or mitigating banding effects. An input ray at thelower limit of the input beam (1222) is diffracted by the input grating(32) into a TIR path (1224) and absorbed by the light-absorbing film(328) applied to the substrate (327), eliminating or mitigating bandingeffects. An input ray near the central portion of the input beam (1220)is diffracted by the input grating (324) into a TIR path (1225) whichdoes not interact with either of the light-absorbing films (326 & 328)and continues to propagate under TIR until it is extracted by the outputgrating (323) into the output beam (1226).

In many embodiments, a debanding optic is a first light-absorbing filmdisposed adjacent to the edges an input substrate containing an inputgrating and disposed adjacent to an optical substrate, and a secondlight-absorbing film disposed adjacent to the edges a second substrate,attached adjacent to the optical substrate opposite the input substrate,such that incident light results in no gaps between successive lightextractions along the TIR ray path, which occurs when the TIR path angleis U as defined by 2D tan (U). Depicted in FIG. 17 is an embodiment of awaveguide device (330) configured such that an input grating (334) isdisposed within an input substrate (333), which together with thesubstrate (332) sandwiches a waveguide (331). The cross section of aninput beam for a given field of view direction (1230) with peripheralrays (1231 & 1232) enters into the input grating (334). An input beamportion bounded by rays (1233 & 1234) is diffracted into a beam path(1236) and intercepted by an absorbing film (335) applied to the edge ofthe upper substrate (332). The input beam portion bounded by rays (1232& 1235) is diffracted into the beam path (1237) undergoes TIR at theouter surface of the upper substrate (332) and intercepted by anabsorbing film (336) applied to the input substrate edge. The input beamportions bounded by rays (1231 & 1233) and (1234 & 1235) are diffractedinto respective TIR paths (1239 &1240) and (1241 & 1242) which exhibitno gap or overlap in the beam cross section region (1243) and at allbeam cross sections thereafter, thereby eliminating banding utilizing aTIR angle U and a waveguide substrate thickness D is given by 2D tan(U). In some particular embodiments, the thickness of a waveguide is 3.4mm, the thickness of an upper substrate 0.5 mm, and a lower substratecontains two 0.5 mm thick glass substrates sandwiching an input grating.Based on this geometry and the debanding condition of a TIR angle U anda waveguide substrate thickness D is given by 2D tan (U), the throughputefficiency is estimated to be roughly 1−2*0.5/(2*3.4)=84% with somesmall variation across the field of view.

In some embodiments utilizing an input substrate, an input grating isimplemented in separate cells bonded to the main waveguide, thussimplifying indium tin oxide (ITO) coating. In many embodimentsutilizing an input substrate, beam shifting techniques based on forminga projected stop and tilting the PGU exit pupil are incorporated, toprovide debanding in orthogonal directions.

Depicted in FIG. 18 is a detail of an embodiment of a waveguide device340 having a waveguide portion (341), a prism (342) with two refractingfaces inclined at a relative angle (1250) and an exit pupil (343) of aPGU (not pictured), the exit pupil (343) tilted at an angle (1251)relative to a reference axis (1252).

In some embodiments, a prism is separated from a waveguide by a smallair gap. In many embodiments, a prism is separated from a waveguide by athin layer of low index material.

Returning to FIG. 18, light beams (1253 & 1254) from the exit pupil(343) correspond to two different field angles refracted through theprism (342) as beams (1255 & 1256) and are then coupled into the TIRpaths (1257 & 1258) inside the waveguide (341). The beam widths at thewaveguide surface adjacent the prism (1259A & 1259B) are depicted. Bychoosing suitable values for the prism angle, PGU exit pupil tilt angle,prism index, waveguide index and waveguide thickness, utilizing a TIRangle U and a waveguide substrate thickness D is given by 2D tan (U),light is debanded for all field angles while at the same time providingan approximately linear relationship between the field angle at the PGUexit pupil and the TIR angle within the waveguide for any ray in thefield of view.

In a number of embodiments incorporating color waveguides, projectedstops are required to be created in different waveguides, each on adifferent plane, such that the waveguides form a stack. Misalignment ofthese stops leads to misregistration of the color components of theoutput images from the waveguide and hence color banding. One solution,in accordance with various embodiments, is a waveguide input stop withouter dichroic portions to provide some compensation for the colorbanding and an inner phase compensation coating (e.g., SiO₂) tocompensate for the phase shift due to the input stop. In someembodiments, a waveguide input stop has outer dichroic portions, butlacks a phase compensation coating. A waveguide input stop, inaccordance with several embodiments, is formed on a thin transparentplate adjacent to an input surface of the waveguide, overlapping aninput grating. In multiple embodiments, a waveguide input stop isdisposed within a layer inside a grating. In many embodiments, awaveguide input stop is disposed directly adjacent to a waveguideexternal surface.

When pupils project at different positions along an optical substrate,in accordance with various embodiments, color display applicationprojected stops are created in different planes inside separate red,green and blue transmitting optical substrate layers. In someembodiments, a waveguide input stop includes outer dichroic portions toshift pupil and eliminate or mitigate color banding and an inner phasecompensation coating in inner portions to compensate for the phaseshift. In many embodiments, an inner phase compensation coating is SiO₂.Depicted in FIG. 19 is an embodiment of a waveguide input stop (350)having outer dichroic portions (352 & 353) and inner phase compensationSiO₂ coating (351) to shift pupil and eliminate or mitigate colorbanding.

In numerous embodiments, a debanding optic is an input gratingconfigured such that light has a unique displacement relative to an edgeof the input grating at any given incident light direction to shiftpupil, eliminating or mitigating a banding effect. Displacement of thelight results in a portion of the light beam to fall outside the inputgrating apertures and therefore not being diffracted into a TIR pathinside a waveguide, which varies with field angle. In severalembodiments, non-diffracted light can be trapped by a suitable absorbingfilm. In many embodiments, a beam width can be tailored by displacementto meet the debanding condition a TIR angle U and a waveguide substratethickness D is given by 2D tan (U). Depicted in FIG. 20 is a detail ofan embodiment of a waveguide device (360) having an optical substrate(361), which contains an input grating (362). Collimated input ray paths(1090 & 1091) and (1092 & 1093) for two different input angles arediffracted into rays (1094 & 1095) and (1096 & 1097). For each inputbeam angle, a portion of the input beam misses the input grating (362)and passes undeviated through the waveguide substrate (361) as exitingrays (1098 and 1099) from each beam. In many embodiments, a lightabsorbing film applied to the waveguide surface traps non-diffractedlight

It should be understood, that the various embodiments of debandingdescribed herein, can be combined. In several embodiments, embodimentsfor debanding can be combined with a technique to vary the diffractionefficiency of the input grating along a principal waveguide direction.Furthermore, in many embodiments, embodiments of debanding are performedin each beam expansion direction. Accordingly, in some embodiments, twoor more of embodiments employing debanding solutions are combined toprovide debanding in two dimensions. In a number of embodiments in whicha waveguide device operates in two dimensions, the device includes foldgratings, which allow for debanding in two dimensions.

In a number of embodiments, a waveguide display is integrated within awindow, for example, a windscreen-integrated HUD for road vehicleapplications. It should be understood that any appropriatewindow-integrated display may be integrated into a waveguide display andfall within various embodiments of the invention. Examples ofwindow-integrated displays are described in U.S. Provisional PatentApplication No. 62/125,064 entitled OPTICAL WAVEGUIDE DISPLAYS FORINTEGRATION Ind. WINDOWS and U.S. Provisional Patent Application No.62/125,066 entitled OPTICAL WAVEGUIDE DISPLAYS FOR INTEGRATION Ind.WINDOWS.

In many embodiments, a waveguide display includes gradient index (GRIN)wave-guiding components for relaying image content between an inputimage generator and the waveguide. Exemplary GRIN wave-guidingcomponents are described in U.S. Provisional Patent Application No.62/123,282 entitled NEAR EYE DISPLAY USING GRADIENT INDEX OPTICS andU.S. Provisional Patent Application No. 62/124,550 entitled WAVEGUIDEDISPLAY USING GRADIENT INDEX OPTICS. In several embodiments, a waveguidedisplay incorporates a light pipe for providing beam expansion in onedirection. Examples of light pipes are described in U.S. ProvisionalPatent Application No. 62/177,494 entitled WAVEGUIDE DEVICEINCORPORATING A LIGHT PIPE. In some embodiments, the input imagegenerator may be based on a laser scanner as disclosed in U.S. Pat. No.9,075,184 entitled COMPACT EDGE ILLUMINATED DIFFRACTIVE DISPLAY. Variousembodiments of the invention are used in wide range of displays,including (but not limited t) HMDs for AR and VR, helmet mounteddisplays, projection displays, heads up displays (HUDs), Heads DownDisplays, (HDDs), autostereoscopic displays and other 3D displays. Anumber of the embodiments are applied in waveguide sensors such as, forexample, eye trackers, fingerprint scanners, LIDAR systems, illuminatorsand backlights.

In some embodiments, a waveguide device incorporates an eye tracker. Itshould be understood that a number of eye trackers can be used and stillfall within various embodiments of the invention, including eye trackersdescribed in PCT/GB2014/000197 entitled HOLOGRAPHIC WAVEGUIDE EYETRACKER, PCT/GB2015/000274 entitled HOLOGRAPHIC WAVEGUIDEOPTICALTRACKER, and PCT Application No.:GB2013/000210 entitled APPARATUSFOR EYE TRACKING.

It should be emphasized that the drawings are exemplary and that thedimensions have been exaggerated. For example, thicknesses of the SBGlayers have been greatly exaggerated. Optical devices based on any ofthe above-described embodiments may be implemented using plasticsubstrates using the materials and processes disclosed in PCTApplication No.: PCT/GB2012/000680, entitled IMPROVEMENTS TO HOLOGRAPHICPOLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES. In someembodiments, the dual expansion waveguide display may be curved.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (for example, variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, positions of elements may be reversedor otherwise varied and the nature or number of discrete elements orpositions may be altered or varied. Accordingly, all such modificationsare intended to be included within the scope of the present disclosure.The order or sequence of any process or method steps may be varied orre-sequenced according to alternative embodiments. Other substitutions,modifications, changes, and omissions may be made in the design,operating conditions and arrangement of the exemplary embodimentswithout departing from the scope of the present disclosure.

DOCTRINE OF EQUIVALENTS

As can be inferred from the above discussion, the above-mentionedconcepts can be implemented in a variety of arrangements in accordancewith embodiments of the invention. Accordingly, although the presentinvention has been described in certain specific aspects, manyadditional modifications and variations would be apparent to thoseskilled in the art. It is therefore to be understood that the presentinvention may be practiced otherwise than specifically described. Thus,embodiments of the present invention should be considered in allrespects as illustrative and not restrictive.

What is claimed is:
 1. A waveguide device comprising: at least oneoptical substrate; at least one light source; at least one light couplercapable of coupling incident light from the light source with an angularbandwidth into a total internal reflection (TIR) within the at least oneoptical substrate such that a unique TIR angle is defined by each lightincidence angle as determined at an input grating; at least one lightextractor for extracting the light from the optical substrate; and adebanding optic capable of mitigating banding effects of an illuminatedpupil, such that the extracted light is a substantially flatillumination profile having mitigated banding, wherein the debandingoptic provides an effective input aperture W such that when the opticalsubstrate has a thickness D, the effective input aperture W isconfigured to provide a TIR angle U in the optical substrate, andwherein the TIR angle U, the effective input aperture W, and thethickness D are related by W=2D tan (U).
 2. The waveguide device ofclaim 1, wherein the extracted light has a spatial non-uniformity lessthan one of either 10% or 20%.
 3. The waveguide device of claim 1,wherein the debanding optic provides spatial variation of the lightalong the TIR path of at least one of diffraction efficiency, opticaltransmission, polarization, or birefringence.
 4. A waveguide devicecomprising: at least one optical substrate; at least one light source;at least one light coupler capable of coupling incident light from thelight source with an angular bandwidth into a total internal reflection(TIR) within the at least one optical substrate such that a unique TIRangle is defined by each light incidence angle as determined at an inputgrating; at least one light extractor for extracting the light from theoptical substrate; and a debanding optic capable of mitigating bandingeffects of an illuminated pupil, such that the extracted light is asubstantially flat illumination profile having mitigated banding,wherein the debanding optic is at least one grating selected from atleast one input grating and at least one output grating, and wherein theselected at least one grating is configured as one or more index layersdisposed within the optical substrate such that the one or more indexlayers influences the light ray paths within the optical substrate as afunction of at least one of ray angle or ray position, shifting theilluminated pupil to mitigate banding effects.
 5. The waveguide deviceof claim 1, further comprising at least one reflecting surface on atleast a part of an edge of the optical substrate, and wherein thedebanding optic comprises one or more index layers disposed adjacent tothe at least one reflecting surface such that the one or more indexlayers are configured to perform a pupil shift to mitigate bandingeffects.
 6. A waveguide device comprising: at least one opticalsubstrate; at least one light source; at least one light coupler capableof coupling incident light from the light source with an angularbandwidth into a total internal reflection (TIR) within the at least oneoptical substrate such that a unique TIR angle is defined by each lightincidence angle as determined at an input grating; at least one lightextractor for extracting the light from the optical substrate; and adebanding optic capable of mitigating banding effects of an illuminatedpupil, such that the extracted light is a substantially flatillumination profile having mitigated banding, wherein the debandingoptic comprises one or more index layers disposed within the opticalsubstrate such that the one or more index layers are configured toperform a pupil shift to mitigate banding effects.
 7. A waveguide devicecomprising: at least one optical substrate; at least one light source;at least one light coupler capable of coupling incident light from thelight source with an angular bandwidth into a total internal reflection(TIR) within the at least one optical substrate such that a unique TIRangle is defined by each light incidence angle as determined at theinput grating; at least one light extractor for extracting the lightfrom the optical substrate; and a debanding optic capable of mitigatingbanding effects of an illuminated pupil, such that the extracted lightis a substantially flat illumination profile having mitigated banding,wherein the debanding optic comprises a plurality of refractive indexlayers that provide spatial variation along each TIR path of at leastone of diffraction efficiency, optical transmission, polarization, orbirefringence to influence ray paths within the optical substrate as afunction of at least one of ray angle or ray position within the opticalsubstrate, resulting in a shift of pupil to mitigate banding effects. 8.The waveguide device of claim 1, wherein the debanding optic comprisesat least one selected from the group consisting of: at least one gratingselected from at least one input grating and at least one outputgrating, and wherein the selected at least one grating is configured toprovide at least two separate waveguide paths which cancelnon-uniformity of light of the extracted light for any incidence lightangle, mitigating banding effects; at least one grating selected from atleast one input grating and at least one output grating, and wherein theselected at least one grating is configured to provide at least twoseparate waveguide paths which cancel non-uniformity of light of theextracted light for any incidence light angle, mitigating bandingeffects, wherein the selected grating has crossed slant gratings used inconjunction with at least one fold grating exit pupil expander; anoptical component within a microdisplay that provides variable effectivenumerical apertures (NA) capable of being spatially varied along atleast one direction to shift pupil shift to mitigate banding effects; aplurality of grating layers within at least one grating of either atleast one input grating or at least one output grating such that theplurality of grating layers is configured to smear out any fixed patternnoise resulting in shift of pupil to mitigate banding effects; and aninput grating configured as an array of selectively switchable elementssuch that configuring the input grating as a switching grating arrayprovides pupil switching in vertical and horizontal directions to shiftpupil to mitigate banding effects.
 9. The waveguide device of claim 1,wherein the debanding optic comprises at least one selected from thegroup consisting of: a microdisplay projecting spatially variednumerical apertures that shift pupil to mitigate banding effects; atilted microdisplay configured to project a tilted, rectangular exitpupil such that the cross section of the exit pupil varies with a fieldangle, such that banding effects are mitigated; a tilted microdisplayconfigured to angle light rays to form various projected pupils atdifferent positions along the optical substrate for each angle ofincident light, such that banding effects are mitigated along oneexpansion axis; a light-absorbing film adjacent to the edges of theoptical substrate such that portions of the incident light, that wouldotherwise give rise to banding, are removed, mitigating banding effects;and an input grating configured such that the light has a uniquedisplacement relative to an edge of the input grating at any givenincident light direction to shift pupil, eliminating or mitigating abanding effect.
 10. The waveguide device of claim 1, wherein the opticalsubstrate has a thickness D, and wherein the debanding optic comprisesat least one selected from the group consisting of: a prism coupled tothe optical substrate, such that a linear relationship between theangles of an exit pupil from the light source and the TIR angles in theoptical substrate result in no gaps between successive light extractionsalong the TIR ray path, which occurs when the TIR path angle is U asdefined by 2D tan (U); a first light-absorbing film disposed adjacent tothe edges an input substrate containing an input grating and disposedadjacent to the optical substrate, and a second light-absorbing filmdisposed adjacent to the edges a second substrate, attached adjacent tothe optical substrate opposite the input substrate, such that incidentlight results in no gaps between successive light extractions along theTIR ray path, which occurs when the TIR path angle is U as defined by 2Dtan (U); and a first light-absorbing film disposed adjacent to the edgesan input substrate containing an input grating and disposed adjacent tothe optical substrate, and a second light-absorbing film disposedadjacent to the edges a second substrate, attached adjacent to theoptical substrate opposite the input substrate, such that incident lightresults in no gaps between successive light extractions along the TIRray path, which occurs when the TIR path angle is U as defined by 2D tan(U), wherein the thickness of the optical substrate is 3.4 mm, thethickness of the second is substrate 0.5 mm, and the input substratecontains two 0.5 mm thick glass substrates sandwiching the inputgrating.
 11. The waveguide device of claim 1, wherein the device isintegrated into a display selected from the group of head mounteddisplay (HMD) and a head up display (HUD).
 12. The waveguide device ofclaim 11, wherein at least one of the following: a human eye ispositioned with an exit pupil of the display; and the deviceincorporates an eye tracker.
 13. The waveguide device of claim 1 furthercomprising an input image generator that further comprises the lightsource, a microdisplay panel, and optics for collimating the light. 14.The waveguide device of claim 1, wherein the light source is selectedfrom the group of: at least one laser, and at least one light emittingdiode (LED).
 15. The waveguide device of claim 1, wherein the lightcoupler is selected from the group of an input grating; and a prism. 16.The waveguide device of claim 1, wherein the light extractor is anoutput grating.
 17. A method to mitigate banding in an outputillumination of a waveguide device, comprising: producing incident lightfrom a light source; passing the incident light through a light couplerto couple the incident light into an optical substrate such that thecoupled light undergoes total internal reflection (TIR) within theoptical substrate; and extracting the TIR light from the opticalsubstrate via a light extractor to produce the output illumination;wherein the light passes through a debanding optic of the waveguidedevice such that the debanding optic mitigates a banding effect of theoutput illumination, wherein the debanding optic comprises an effectiveinput aperture W such that the optical substrate has a thickness D, theeffective input aperture W is configured to provide a TIR angle U in theoptical substrate, and wherein the TIR angle U, the effective inputaperture W, and the thickness D are related by W=2D tan (U).
 18. Themethod of claim 17, wherein the output illumination has a spatialnon-uniformity less than one of either 10% or 20%.
 19. The method ofclaim 17, wherein the debanding optic provides spatial variation of theTIR light along the TIR path of at least one of diffraction efficiency,optical transmission, polarization, or birefringence.
 20. The method ofclaim 17, wherein the waveguide device further comprises at least onereflecting surface on at least a part of an edge of the opticalsubstrate, and wherein the debanding optic further comprises one or moreindex layers disposed adjacent to the at least one reflecting surfacesuch that the one or more index layers are configured to shift pupil tomitigate banding effects.
 21. A method to mitigate banding in an outputillumination of a waveguide device, comprising: producing incident lightfrom a light source; passing the incident light through a light couplerto couple the incident light into an optical substrate such that thecoupled light undergoes total internal reflection (TIR) within theoptical substrate; and extracting the TIR light from the opticalsubstrate via a light extractor to produce the output illumination;wherein the light passes through a debanding optic of the waveguidedevice such that the debanding optic mitigates a banding effect of theoutput illumination, wherein the debanding optic comprises one or moreindex layers disposed within the optical substrate such that the one ormore index layers are configured to perform a pupil shift to mitigatebanding effects.
 22. The method of claim 17, wherein the opticalsubstrate has a configuration selected from the group consisting of:wherein the debanding optic further comprises a prism coupled to theoptical substrate, such that a linear relationship between the angles ofan exit pupil from the light source and the TIR angles in the opticalsubstrate result in no gaps between successive light extractions alongthe TIR ray path; and wherein the debanding optic further comprises afirst light-absorbing film disposed adjacent to the edges of an inputsubstrate containing an input grating and disposed adjacent to theoptical substrate, and a second light-absorbing film disposed adjacentto the edges a second substrate, attached adjacent to the opticalsubstrate opposite the input substrate, such that incident light resultsin no gaps between successive light extractions along the TIR ray path;and wherein the debanding optic further comprises a firstlight-absorbing film disposed adjacent to the edges of an inputsubstrate containing an input grating and disposed adjacent to theoptical substrate, and a second light-absorbing film disposed adjacentto the edges a second substrate, attached adjacent to the opticalsubstrate opposite the input substrate, such that incident light resultsin no gaps between successive light extractions along the TIR ray path,and wherein the thickness of the optical substrate is 3.4 mm, thethickness of the second is substrate 0.5 mm, and the input substratecontains two 0.5 mm thick glass substrates sandwiching the inputgrating.
 23. The method of claim 17, wherein the method is performed bya display selected from the group of head mounted display (HMD) and ahead up display (HUD).
 24. The method of claim 23, wherein at least oneof: a human eye is positioned with an exit pupil of the display and thedisplay incorporates an eye tracker.
 25. The method of claim 17, whereinthe waveguide device further comprises an input image generator thatfurther comprises the light source, a microdisplay panel, and optics forcollimating the light.
 26. The method of claim 17, wherein the lightsource is selected from the group of: at least one laser; and at leastone light emitting diode (LED).
 27. The method of claim 17, wherein thelight coupler is selected from one of: an input grating; and a prism.28. The method of claim 17, wherein the light extractor is an outputgrating.
 29. A waveguide device comprising: at least one opticalsubstrate; at least one light source; at least one light coupler capableof coupling incident light from the light source with an angularbandwidth into a total internal reflection (TIR) within the at least oneoptical substrate such that a unique TIR angle is defined by each lightincidence angle as determined at the input grating; at least one lightextractor for extracting the light from the optical substrate; and adebanding optic capable of mitigating banding effects of an illuminatedpupil, such that the extracted light is a substantially flatillumination profile having mitigated banding, wherein the debandingoptic is at least one grating selected from at least one input gratingand at least one output grating, and wherein the selected at least onegrating is configured as one or more index layers disposed within theoptical substrate such that the one or more index layers influences thelight ray paths within the optical substrate as a function of at leastone of ray angle or ray position, shifting pupil to mitigate bandingeffects, and wherein at least one index layer of the one or more indexlayers is a gradient index (GRIN) medium.
 30. A waveguide devicecomprising: at least one optical substrate; at least one light source;at least one light coupler capable of coupling incident light from thelight source with an angular bandwidth into a total internal reflection(TIR) within the at least one optical substrate such that a unique TIRangle is defined by each light incidence angle as determined at theinput grating; at least one light extractor for extracting the lightfrom the optical substrate; and a debanding optic capable of mitigatingbanding effects of an illuminated pupil, such that the extracted lightis a substantially flat illumination profile having mitigated banding,wherein the debanding optic comprises a plurality of refractive indexlayers that provide spatial variation along each TIR path of at leastone of diffraction efficiency, optical transmission, polarization, orbirefringence to influence ray paths within the optical substrate as afunction of at least one of ray angle or ray position within the opticalsubstrate, resulting in shift of pupil to mitigate banding effects, andwherein the plurality of refractive index layers incorporates adhesivesof different indices.
 31. A waveguide device comprising: at least oneoptical substrate; at least one light source; at least one light couplercapable of coupling incident light from the light source with an angularbandwidth into a total internal reflection (TIR) within the at least oneoptical substrate such that a unique TIR angle is defined by each lightincidence angle as determined at the input grating; at least one lightextractor for extracting the light from the optical substrate; and adebanding optic capable of mitigating banding effects of an illuminatedpupil, such that the extracted light is a substantially flatillumination profile having mitigated banding, wherein the debandingoptic comprises a plurality of refractive index layers that providespatial variation along each TIR path of at least one of diffractionefficiency, optical transmission, polarization, or birefringence toinfluence ray paths within the optical substrate as a function of atleast one of ray angle or ray position within the optical substrate,resulting in shift of pupil to mitigate banding effects, and wherein theplurality of refractive index layers incorporates layers selected fromthe group consisting of alignment layers, isotropic refractive layers,GRIN structures, antireflection layers, partially reflecting layer, andbirefringent stretched polymer layers.
 32. A method to mitigate bandingin an output illumination of a waveguide device, comprising: producingincident light from a light source; passing the incident light through alight coupler to couple the incident light into an optical substratesuch that the coupled light undergoes total internal reflection (TIR)within the optical substrate; and extracting the TIR light from theoptical substrate via a light extractor to produce the outputillumination; wherein the light passes through a debanding optic of thewaveguide device such that the debanding optic mitigates a bandingeffect of the output illumination, wherein the debanding optic comprisesone or more index layers disposed within the optical substrate such thatthe one or more index layers influences the light ray paths within theoptical substrate as a function of at least one of ray angle or rayposition, resulting in a shift of pupil to mitigate banding effects. 33.A method to mitigate banding in an output illumination of a waveguidedevice, comprising: producing incident light from a light source;passing the incident light through a light coupler to couple theincident light into an optical substrate such that the coupled lightundergoes total internal reflection (TIR) within the optical substrate;and extracting the TIR light from the optical substrate via a lightextractor to produce the output illumination; wherein the light passesthrough a debanding optic of the waveguide device such that thedebanding optic mitigates a banding effect of the output illumination,wherein the debanding optic comprises one or more index layers disposedwithin the optical substrate such that the one or more index layersinfluences the light ray paths within the optical substrate as afunction of at least one of ray angle or ray position, resulting in ashift of pupil to mitigate banding effects, wherein at least one indexlayer of the one or more index layers is a gradient index (GRIN) medium.34. A method to mitigate banding in an output illumination of awaveguide device, comprising: producing incident light from a lightsource; passing the incident light through a light coupler to couple theincident light into an optical substrate such that the coupled lightundergoes total internal reflection (TIR) within the optical substrate;and extracting the TIR light from the optical substrate via a lightextractor to produce the output illumination; wherein the light passesthrough a debanding optic of the waveguide device such that thedebanding optic mitigates a banding effect of the output illumination,wherein the debanding optic comprises a plurality of refractive indexlayers that provide spatial variation along each TIR path of at leastone of diffraction efficiency, optical transmission, polarization, orbirefringence to influence ray paths within a waveguide substrate as afunction of at least one of ray angle or ray position within thesubstrate, resulting in shift of pupil to mitigate banding effects. 35.A method to mitigate banding in an output illumination of a waveguidedevice, comprising: producing incident light from a light source;passing the incident light through a light coupler to couple theincident light into an optical substrate such that the coupled lightundergoes total internal reflection (TIR) within the optical substrate;and extracting the TIR light from the optical substrate via a lightextractor to produce the output illumination; wherein the light passesthrough a debanding optic of the waveguide device such that thedebanding optic mitigates a banding effect of the output illumination,wherein the debanding optic comprises a plurality of refractive indexlayers that provide spatial variation along each TIR path of at leastone of diffraction efficiency, optical transmission, polarization, orbirefringence to influence ray paths within the optical substrate as afunction of at least one of ray angle or ray position within thesubstrate, resulting in shift of pupil to mitigate banding effects, andwherein the plurality of refractive index layers incorporates adhesivesof different indices.
 36. A method to mitigate banding in an outputillumination of a waveguide device, comprising: producing incident lightfrom a light source; passing the incident light through a light couplerto couple the incident light into an optical substrate such that thecoupled light undergoes total internal reflection (TIR) within theoptical substrate; and extracting the TIR light from the opticalsubstrate via a light extractor to produce the output illumination;wherein the light passes through a debanding optic of the waveguidedevice such that the debanding optic mitigates a banding effect of theoutput illumination, wherein the debanding optic comprises a pluralityof refractive index layers that provide spatial variation along each TIRpath of at least one of diffraction efficiency, optical transmission,polarization, or birefringence to influence ray paths within the opticalsubstrate as a function of at least one of ray angle or ray positionwithin the substrate, resulting in shift of pupil to mitigate bandingeffects, wherein the plurality of refractive index layers incorporatelayers selected from the group consisting of alignment layers, isotropicrefractive layers, GRIN structures, antireflection layers, partiallyreflecting layer, and birefringent stretched polymer layers.